Seongnam, Gyeonggi Province (South Korea)

While in South Korea, we traveled to the city of Seongnam (Sŏngnam-si), just southeast of Seoul in Gyeonggi Province. While there, we passed a flag display at an intersection of two major highways. There were dozens of flags, including the South Korean national flag, the new Gyeonggi Province flag, and the city flag of Seongnam.
The Seongnam city flag features the city logo (a stylized blue and red flower) on a white field, with the name of the city (Seongnam-si, 성남시) written in black Hangul beneath the logo.
Randy Young, 28 November 2014

"(The official symbol is the) royal azalea which is flower of the city, around Namhansanseong Fortress in the 21st century which represents the development of a new city as well as the beginning Seongnam city developing harmoniously:

• 5 Petals of Royal Azalea: Defines the harmonious development of economy, society, culture, education and welfare
• Fortress (Inside the Royal Azalea): Portrays Namhansanseong Fortress, defining the noble spirit of Seongnam City wisely succeeding the traditions of the history and preparing for a future filled with hope
• Pillar (Inside the oval): Symbolizes Seongnam City developing into a modern city and taking a great leap forward dynamically
• Red: Lively Seongnam City with promising development
• Yellow: Friendly Seongnam City developing by succeeding the traditions of the history
• Blue: Pleasant Seongnam City with clear and green environment"

Source: http://www.seongnam.go.kr/EN/government/symbols/page.do
For additional information go to Seongnam (official website): http://www.seongnam.go.kr/
Esteban Rivera, 25 May 2017

Here is better image of flag and also few more flag variants.
http://u20worldcup.kbs.co.kr/news/view.do?ncd=3646210
Tomislav Šipek, 31 August 2019

"성남도시개발공사,'무재해 (English: Seongnam Urban Development Corporation) is a government agency from the city of Seongnam in charge of developing urban areas".

Its flag is the logo (https://pbs.twimg.com/profile_images/804482294316548096/5H-V4Dko.jpg)
over a white horizontal flag, seen here (flag on the right):
http://www.mtime.co.kr/news/photo/201509/3008_950_1116.JPG
(source: http://www.mtime.co.kr/news/articleView.html?idxno=3008)
Esteban Rivera, 25 May 2017